Microlithographic imaging optical system including multiple mirrors

ABSTRACT

An imaging optical system includes a plurality of mirrors configured to image an object field in an object plane of the imaging optical system into an image field in an image plane of the imaging optical system. An illumination system includes such an imaging optical system. The transmission losses of the illumination system are relatively low.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and claims benefit under 35 USC120 to, international application PCT/EP2009/006171, filed Aug. 26,2009, which claims benefit of German Application No. 10 2008 046 699.9,filed Sep. 10, 2008 and U.S. Ser. No. 61/095,689, filed Sep. 10, 2008.International application PCT/EP2009/006171 is hereby incorporated byreference in its entirety.

FIELD

The disclosure relates to an imaging optical system with a plurality ofmirrors, which image an object field in an object plane into an imagefield in an image plane.

BACKGROUND

Imaging optical systems of this type are known from EP 1 093 021 A2 andWO 2006/069725 A1. Further imaging optical systems are known from US2007/0035814 A1, U.S. Pat. No. 7,186,983 B2, US 2007/0233112 A1 and WO2006/037 651 A1. An imaging optical system is known from U.S. Pat. No.6,172,825 B1, in which the position of an entry pupil plane of theimaging optical systems is produced from the position for an aperturediaphragm or stop AS.

SUMMARY

The disclosure provides illumination system including an imaging opticalsystem in which the transmission losses of the illumination system arerelatively low.

In some embodiments, an imaging optical system has a beam path, anobject plane, an image plane and an entry pupil. The imaging opticalsystem also has a connecting axis, which is perpendicular to the objectplane and runs through the geometric centre point of the mirror which ismost closely adjacent to the object field. The mirror which is mostclosely adjacent to the object field is arranged at a spacing from theobject field which is greater than a spacing of an entry pupil plane ofthe imaging optical system from the object field. The pupil plane liesin the beam path of the imaging light up-stream of the object field.

The imaging optical system includes a plurality of mirrors that image anobject field in an object plane into an image field in the image planealong the beam path. A connecting axis is perpendicular to the objectplane and runs through the geometric centre point of the mirror which ismost closely adjacent to the object field. The distance between theobject field and the mirror which is most closely adjacent to the objectfield is greater than the distance between the object field and theentry pupil plane. The entry pupil plane lies in the beam path up-streamof the object field.

In certain embodiments, an imaging optical system with a plurality ofmirrors, which image an object field in an object plane into an imagefield in an image plane, where:

-   -   an entry pupil plane lies in the beam path of the imaging light        upstream of the object field,    -   the imaging light is reflected on the object plane,    -   a connecting axis is perpendicular to the object plane and runs        through the geometric center point of the entry pupil,    -   an intersection point of the connecting axis with the entry        pupil plane is closer to the object plane than a first        intersection point in the beam path of the imaging light        downstream of the object field, of a main beam of a central        object field point with the connecting axis,    -   at least one of the mirrors has a through-opening for imaging        light to pass through.

In an imaging optical system of this type, when using a reflectingobject to be imaged, an optical component may be arranged in the beampath upstream of the object field on the connecting axis. As a result,the number of components used to illuminate the object field, of anoptical illumination system arranged in the beam path upstream of theimaging optical system can be reduced, so the total losses ofillumination light are reduced.

The disclosure also provides to develop an imaging optical system of thetype mentioned at the outset in such a way that deformations of a mirroradjacent to a field have effects, which are as small as possible, on theimaging behaviour of the imaging optical system.

This can be achieved according to the disclosure by an imaging opticalsystem of the type mentioned at the outset, the imaging optical system,spaced apart from a first mirror, which is most closely adjacent to oneof the two fields and is called the neighboring mirror, having adeformable further mirror, which is arranged in a plane, which isoptically conjugated to an arrangement plane of the neighboring mirrorin the imaging optical system. Examples of planes optically conjugatedwith respect to one another of an imaging optical system are the fieldplanes of the imaging optical system or the pupil planes of the imagingoptical system. All planes, which correspond to one another with regardto the bundle form and the angle distribution of the imaging beams, areplanes which are optically conjugated with respect to one another.

According to the disclosure, it was recognized that a deformable mirrorin an optically conjugated plane with respect to the neighboring mirror,the deformation of which brings about undesired changes in theproperties of the imaging optical system, leads to good compensation ofchanges in the imaging properties caused because of the deformation. Inthis case, deformations of the neighboring mirror, which may havevarious causes, can be compensated. Deformations of the neighboringmirror because of its inherent weight, in other words gravitativedeformations, may be compensated. Deformations of the neighboring mirrorcan also be compensated by the further mirror arranged in the opticallyconjugated plane, these being produced by oscillations of theneighboring mirror. In this case, the deformable mirror may be equippedwith actuating elements, which allow a deformation which is synchronisedwith the oscillations of the neighboring mirror. The deformable mirrormay, for example, be actuatable at a bandwidth corresponding to thebandwidth of the oscillation of the neighboring mirror. An example ofactuating elements which can be used for this in the deformable mirroris described in U.S. Pat. No. 7,443,619 B2. The actuating elementsdisclosed there, which are used for the deformation of the reflectionsurface of a mirror, may be operated at a bandwidth, which is so highthat compensation of deformations induced by oscillation in theneighboring mirror is thereby possible. In particular, Lorentz actuatorsmay be used. Thermal deformations of the neighboring mirror may also becompensated with the aid of the deformable mirror arranged in theoptically conjugated plane.

A further object of the present disclosure is to develop an imagingoptical system of the type mentioned at the outset in such a way that aspacing, which is as small as possible, of a reflection surface of afield-adjacent mirror from the adjacent field is possible.

This object is achieved according to the disclosure by an imagingoptical system of the type mentioned at the outset, wherein a supportbody of a mirror, which is most closely adjacent to one of the twofields, which is also called a neighboring mirror, is made of amaterial, the modulus of elasticity of which is at least twice as greatas the modulus of elasticity of the material of the support body of atleast one of the other mirrors.

According to the disclosure, it was recognized that it is certainlypossible to use a material with a very high modulus of elasticity in thematerial selection for the neighboring mirror. This allows theneighboring mirror to be equipped with a very thin support body, whichcan be brought correspondingly closely to the field. Because of the highmodulus of elasticity of the material of the support body of theneighboring mirror, the latter, despite the optionally very thin supportbody, has adequate stability. The support bodies of the other mirrors,which may be thicker, in other words less thin, may, on the other hand,be made of a material with a lower modulus of elasticity. The materialselection for these other mirrors may therefore take place from otherpoints of view. These other mirrors may all be manufactured from thesame material; this is however not imperative. The modulus of elasticityof the neighboring mirror may be at least twice as great as the greatestmodulus of elasticity of the material of the support bodies of all theother mirrors. The comparative material, with which the material of theneighboring mirror is compared with respect to the modulus ofelasticity, is then the material of the other mirror with the greatestmodulus of elasticity. When using the imaging optical system as aprojection lens system for transmitting a structure arranged in theobject field into the image field, the neighboring mirror is mostclosely adjacent to the image field of the imaging optical system.Another application of the imaging optical system is a microscope lenssystem. In this case, the neighboring mirror is most closely adjacent tothe object field of the imaging optical system. Generally, theneighboring mirror is most closely adjacent to the field on thehigh-aperture side of the imaging optical system. No other mirror of theimaging optical system thus has a smaller spacing from this field.

The features of the imaging optical systems according to the disclosuredescribed above may also be implemented in combination.

The neighboring mirror may be manufactured from a material with amodulus of elasticity which is at least 150 GPa. A modulus of elasticityof this type allows a very thin design of the support body of theneighboring mirror. The support body of the neighboring mirror ispreferably made of a material with a modulus of elasticity which is atleast 200 GPa, more preferably at least 250 GPa, more preferably 300GPa, more preferably 350 GPa and still more preferably 400 GPa.

The support body of the neighboring mirror may also be manufactured fromsilicon carbide. This material, for example, allows production of a verythin support body via a forming method by a graphite forming body. Thesupport body can then be still further processed using known surfaceprocessing methods, if this becomes desirable to achieve the opticalimaging quality. Alternative materials for the support body of theneighboring mirror are SiSiC, CSiC and SiN.

The imaging optical system, spaced apart from the neighboring mirror,may have a deformable mirror. With the aid of a deformable mirror ofthis type, a compensation of thermal deformations of the neighboringmirror is possible, which may, for example, come from a thermal loadingof the neighboring mirror by residual absorption of the imaging light.

The deformable mirror may be arranged in an optical plane which isconjugated with respect to the arrangement plane of the neighboringmirror in the imaging optical system. This simplifies the compensationof thermal deformations of the neighboring mirror by a compensatingdeformation of the deformable mirror, as measured deformations of theneighboring mirror can easily be converted into compensatingdeformations of the deformable mirror. In this case, it is sufficient tomake a single mirror of the imaging optical system deformable tocompensate thermal deformations of the neighboring mirror.Alternatively, it is naturally also possible to make a plurality ofmirrors of the imaging optical system deformable in a targeted manner.

The mirrors, which the imaging optical system has in addition to theneighboring mirror, may be constructed from a material with a thermalexpansion coefficient, which is at most 1×10⁻⁷ m/m/K. Examples ofmaterials of this type are Zerodur® and ULE®. A thermal load on mirrorsmade of these materials practically does not lead to any or only veryslight deformation of the reflection surfaces thereof.

If the imaging optical system has precisely six mirrors, this allows asimultaneously compact and, with regard to its imaging errors, wellcorrected imaging optical system.

A reflection surface of at least one mirror of the imaging opticalsystem may be designed as a surface which can be described by arotationally symmetrical asphere. As a result, good imaging errorcorrection is made possible.

A reflection surface of at least one mirror of the imaging opticalsystem may be designed as a freeform surface which cannot be describedby a rotationally symmetrical function. The use of freeform surfacesinstead of reflection surfaces having a rotationally symmetrical axisprovides new degrees of design freedom, which leads to imaging opticalsystems with feature combinations which could not be realised withrotationally symmetrical reflection surfaces. Freeform surfaces suitablefor use in imaging optical systems according to the disclosure are knownfrom US 2007/0058269 A1 and US 2008/0170310 A1.

At least one of the mirrors of the imaging optical system may have athrough-opening for imaging light to pass through. This allows thedesign of the imaging optical system with a very large numericalaperture. When using the imaging optical system as a projection lenssystems, a very high structure resolution at the given wavelength of theimaging light may thus be achieved.

The advantages of a projection exposure system with an imaging opticalsystem according to the disclosure, a light source for the illuminationand imaging light and with an illumination optical system for guidingthe illumination light to the object field of the imaging opticalsystem, and in particular the advantages of a projection exposuresystem, in which a pupil facet mirror of the optical illumination systemis arranged in an entry pupil plane of the imaging optical system,correspond to those, which were stated above in relation to the imagingoptical system according to the disclosure. In an arrangement of thepupil facet mirror in the entry pupil plane of the imaging opticalsystem, the pupil facet mirror can direct the illumination and imaginglight directly to the object field. Optical components lying in between,between the pupil facet mirror and the object field are not thennecessary and this increases the transmission of the projection exposuresystem. This is advantageous, in particular, when the illumination andimaging light can generally only be guided with losses, which is thecase, for example, in EUV wavelengths in the range between 5 nm and 30nm. If the imaging optical system according to the disclosure isdesigned such that, on a connecting axis, which is perpendicular to theobject plane and runs through the geometric center point of the mirror,which is most closely adjacent to the object field, the mirror mostclosely adjacent to the object field is arranged at a spacing, which isgreater than a spacing of an entry pupil plane located in the beam pathof the imaging light upstream of the object field, of the imagingoptical system from the object field, when using a reflecting object tobe imaged, the pupil facet mirror arranged in the entry pupil plane canbe accommodated on the connecting axis and therefore compactly betweenother components of the imaging optical system. The same applies whenthe imaging optical system according to the disclosure is designed suchthat an intersection point of a connecting axis, which is perpendicularto the object plane and runs through the geometric center point of theentry pupil, with the entry pupil plane, lies closer to the object planethan a first intersection point lying in the beam bath of the imaginglight after the object field of a main beam, of a central object fieldpoint with the connecting axis. It is to be noted here that because ofthe fact that the beam path of the illumination or imaging light isreflected on the object plane, the entry pupil plane, although it liesin the beam path upstream of the object plane, comes to rest on the sideof the object plane facing the image plane and generally between theobject plane and the image plane.

The light source of the projection exposure system may be wideband and,for example, have a bandwidth, which is greater than 1 nm, which isgreater than 10 nm or which is greater than 100 nm. In addition, theprojection exposure system may be designed such that it can be operatedby light sources of different wavelengths. An optical illuminationsystem with a pupil facet mirror is, for example, known fromUS2007/0223112 A1.

Corresponding advantages, as stated above, apply to a method forproducing a microstructured component having the following method steps:

-   -   providing a reticle and a wafer,    -   projecting a structure on the reticle onto a light-sensitive        layer of the wafer with the aid of the projection exposure        system according to the disclosure,    -   producing a microstructure on the wafer,        and the microstructured or nanostructured component produced        thereby.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be described in more detail below with the aid of thedrawings, in which:

FIG. 1 schematically shows a projection exposure system formicrolithography;

FIG. 2 shows a meridianal section which contains imaging beam paths offield points spaced apart from one another, through an embodiment of anoptical projection system of the projection exposure system according toFIG. 1; and

FIG. 3 schematically shows a beam path supplemented by an illuminationsystem of the projection exposure system in a projection exposure systemwith a further embodiment of an optical projection system.

DETAILED DESCRIPTION

A projection exposure system 1 for microlithography has a light source 2for illumination light. The light source 2 is an EUV light source, whichgenerates light in a wavelength range of between 5 nm and 30 nm. OtherEUV wavelengths are also possible. Generally any wavelengths, forexample visible wavelengths are even possible for the illumination lightguided in the projection exposure system 1. A beam path of theillumination light 3 is shown very schematically in FIG. 1.

An optical illumination system 6 is used to guide the illumination light3 to an object field 4 in an object plane 5. The object field 4 in animage field 8 in an image plane 9 is imaged at a predetermined reductionscale by an optical projection system 7. The optical projection system 7reduces by a factor of 8.

Other imaging scales are also possible, for example 4×, 5×, 6× or elseimaging scales, which are greater than 8×. For illumination light withEUV wavelengths, an imaging scale of 8× is suitable in particular, asthe angle of incidence on the object side can thus be kept small on areflection mask. Illumination angles on the object side of less than 6°can be realised for an image-side aperture of the optical projectionsystem 7 of NA=0.5, with an imaging scale of 8×. The image plane 9 isarranged in the optical projection system 7 parallel to the object plane5. A section coinciding with the object field 4, of a reflecting mask10, which is also called a reticle, is imaged here. Because of thereflecting effect of the reticle 10, the illumination light 3 isreflected on the object plane 5. The imaging takes place on the surfaceof a substrate 11 in the form of a wafer, which is carried by asubstrate holder 12. FIG. 1 schematically shows between the reticle 10and the optical projection system 7, a beam bundle 13 of theillumination light 3 running into the latter and, between the opticalprojection system 7 and the substrate 11, a beam bundle 14 of theillumination light 3 running out of the optical projection system 7. Theimage field-side numerical aperture NA of the optical projection system7 according to FIG. 2 is 0.50.

To facilitate the description of the projection exposure system 1, aCartesian xyz coordinate system is given in the drawing, from which therespective position relationship of the components shown in the figuresemerges. In FIG. 1, the x-direction runs perpendicularly to the plane ofthe drawing into the latter, and the y-direction runs to the right andthe z-direction runs downwardly.

The projection exposure system 1 is of the scanner type. Both thereticle 10 and the substrate 11 are scanned during operation of theprojection exposure system 1 in the y-direction.

FIG. 2 shows the optical design of the optical projection system 7. Thebeam path is shown, in each case, of three individual beams 15, whichemanate from five object field points lying one above the other in FIG.2 and spaced apart from one another in the y-direction, the threeindividual beams 15, which belong to one of these five object fieldpoints, being associated in each case with three different illuminationdirections for the five object field points. These three illuminationdirections are depicted by the upper coma beam, the lower coma beam andthe main beam of each of the five object field points.

Proceeding from the object plane 5, the individual beams 15 are firstlyreflected by a first mirror M1 and then by further mirrors, which aredesignated below, in the order of the beam path, mirror M2, M3, M4, M5and M6. In each case, the mathematical parent surfaces used to calculatethe form of the reflection surfaces of the mirrors M1 to M6 are shown.In the actual optical projection system 7, the reflection surfaces ofthe mirrors M1 to M6 are actually only present where they are impingedupon by the individual beams 15.

The optical projection system 7 according to FIG. 2 thus has sixreflecting mirrors. These mirrors bear a highly reflective coating forthe wavelength of the illumination light 3, if this is desirable becauseof the wavelength, for example in the EUV. In particular, the mirrors M1to M6 have multi-reflection coatings to optimise their reflection forthe impinging illumination light 3. The reflection is, in particular,when EUV illumination light 3 is used, all the better, the closer thereflection angle, in other words the angle of impingement of theindividual beams 15 on the surfaces of the mirrors M1 to M6, to theperpendicular incidence. The optical projection system 7 overall hassmall reflection angles for all the individual beams 15.

Radiations with very different wavelengths from one another can also beguided in the optical illumination system 6 and the optical projectionsystem 7, as these optical systems have substantially achromaticproperties. It is thus possible, for example, to guide an adjustmentlaser or an auto focusing system in these optical systems, a wavelengthwhich is very different from the working wavelength thereof beingsimultaneously worked with for the illumination light. Thus, anadjusting laser may work at 632.8 nm, at 248 nm or at 193 nm, whileillumination light in the range between 5 and 30 nm is simultaneouslyworked with.

The mirror M3 has a convex basic shape. In other words, the mirror M3can be described by a convex best adapted surface. In the followingdescription, mirrors of this type are designated, in a simplifiedmanner, convex. Mirrors which can be described by a concavely bestadapted surface, are designated, in a simplified manner, concave. Theconvex mirror M3 ensures a good Petzval correction in the opticalprojection system 7.

An overall length of the optical projection system 7, in other words thespacing between the object plane 5 and the image plane 9, is 1521 mm inthe optical projection system 7.

The individual beams 15 belonging to a specific illumination directionof the five object field points combine in a pupil plane 16 of theoptical projection system 7. The pupil plane 16 is arranged adjacent tothe mirror M3 in the beam path thereafter.

The mirrors M1 to M4 image the object plane 5 in an intermediate imageplane 17. The intermediate image-side numerical aperture of the opticalprojection system 7 is about 0.2. The mirrors M1 to M4 form a first partimaging optical system of the optical projection system 7 with areducing imaging scale of about 3.2×. The following mirrors M5 and M6form a further part imaging optical system of the optical projectionsystem 7 with a reducing imaging scale of about 2.5×. Formed in the beampath of the illumination light 3 between the mirrors M4 and M5 upstreamof the intermediate image plane 7 and adjacent thereto is athrough-opening 18 in the mirror M6, through which the illumination orimaging light 3 passes upon the reflection from the fourth mirror M4 tothe fifth mirror M5. The fifth mirror M5 in turn has a centralthrough-opening 19, through which the beam bundle 14 passes between thesixth mirror M6 and the image plane 9.

In the beam path between the fifth mirror M5 and the sixth mirror M6 isa further pupil plane 20 of the optical projection system 7, which isoptically conjugated to the first pupil plane 16. At the site of thefurther pupil plane 20 there exists a diaphragm plane which isphysically accessible from the outside. An aperture diaphragm may bearranged in this diaphragm plane.

The optical projection system 7, in one of the pupil planes 16, 20, hasan obscuration diaphragm or stop arranged in a centered manner. As aresult, the part beams of the projection beam path associated with thecentral through-openings 18, 19 in the mirrors M6, M5 are obscured.Therefore, the design of the optical projection system 7 is also calleda design with a central pupil obscuration.

A distinguished individual beam 15, which connects a central objectfield point with a centrally illuminated point in the entry pupil of theoptical projection system 7 is also called a main beam of a centralfield points. The main beam of the central field point, from thereflection at the sixth mirror M6, with the image plane 9, approximatelyencloses a right angle, in other words, runs approximately parallel tothe z-axis of the projection exposure system 1. This angle is greaterthan 85°.

The image field 8 has the shape of a ring field segment, in other wordsis delimited by two part circles running parallel to one another and twoside edges also running parallel to one another. These side edges run inthe y-direction. Parallel to the x-direction, the image field 8 has anextent of 13 mm. Parallel to the y-direction, the image field 8 has anextent of 1 mm. The radius R of the through-opening 19 satisfies thefollowing relation for a vignetting-free guidance.

$R \geq {{\frac{1}{2} \cdot D} + {d_{w} \cdot {NA}}}$

D is the diagonal here of the image field 8. d_(w) is a free workingspacing of the mirror M5 from the image plane 9. This free workingspacing is defined as the spacing between the image plane 9 and thesection located closest thereto of a used reflection surface of theclosest mirror of the optical projection system 7, in other words, inthe embodiment according to FIG. 2 of the mirror M5, NA is theimage-side numerical aperture. The free working spacing d_(w) in theoptical projection system 7 is 39 mm.

The fifth mirror M5 is the mirror which is most closely adjacent to theobject field 5 in the image plane 9. The fifth mirror M5 is thereforealso called the neighboring mirror below. The neighboring mirror M5 hasa support body 21 which is indicated by dashed lines in FIG. 2, on whichthe reflection surface of the neighboring mirror M5 is formed. Thesupport body 21 is made of silicon carbide. This material has a modulusof elasticity (Young's modulus) of 400 GPa. The other mirrors M1 to M4and M6 of the optical projection system 7 are made of Zerodur®. Thismaterial has a modulus of elasticity of 90 GPa.

The modulus of elasticity of the support body 21 of the neighboringmirror M5 is thus more than twice as great as the modulus of elasticityof the material for the support body 22 of the other mirrors M1 to M4and M6.

The support body 21 has a maximum thickness of 35 mm, so a free workingspacing of 4 mm remains between a rear of the mirror M5 remote from thereflection surface of the mirror M5, and the image plane. A maximumdiameter of the reflection surface used of the mirror M5 in the opticalprojection system 7 is 285 mm. A ratio between this maximum diameter andthe thickness of the support body 21 of the mirror M5 is therefore285/35=8.14. Other ratios of this type, which will also be called aspectratios below are possible in the range between 6 and 20.

The support body 21 of the neighboring mirror M5 may also be made from adifferent material with a modulus of elasticity which is at least 150GPa. Examples of materials of this type are reaction-boundsilicon-infiltrated silicon carbide (SiSiC) with a modulus of elasticityof 395 GPa, carbon fibre-reinforced silicon carbide (CSiC) with amodulus of elasticity of 235 GPa and silicon nitride (SiN) with amodulus of elasticity of 294 GPa. Zerodur®, has, in the room temperaturerange of interest, a thermal expansion coefficient of less than 50×10⁻⁹m/m/K. The support bodies 22 of the mirrors M1 to M4 and M6 may also beconstructed from a different material with a thermal expansioncoefficient, which is at most 1×10⁻⁷ m/m/K. A further example of amaterial of this type is ULE® with a thermal expansion coefficient,which, in the room temperature range of interest, is also less than50×10⁻⁹ m/m/K, and which has a modulus of elasticity of 69 GPa.

The thermal expansion coefficient of the material of the support body 21of the neighboring mirror M5 is significantly greater than the thermalexpansion coefficient of the support bodies 22 of the other mirrors ofthe optical projection system 7. SiC, for example, has a thermalexpansion coefficient in the room temperature range of interest of2.6×10⁻⁶ m/m/K. The thermal expansion coefficients of the other materialvariants for the support body 21 of the neighboring mirror M5 vary in arange between 1×10⁻⁶ m/m/K and 2.6×10⁻⁶ m/m/K.

The neighboring mirror M5 is in an arrangement plane in the imaging beampath of the optical projection system 7, which is optically conjugatedto an arrangement plane, in which the third mirror M3 lies. The mirrorM4 lying in between in the imaging beams path thus acts such that itapproximately images these two arrangement planes of the mirrors M3 andM5 in one another.

The third mirror M3 is designed as a deformable mirror. The reflectionsurface of the third mirror M3 is, in one embodiment of the deformablemirror, connected at the rear to a plurality of actuators 23 actingperpendicularly to the reflection surface, which are connected by signallines or a signal bus 24 to a control device 25. By individualactivation of the actuators 23 by the control device 25, the form of thereflection surface of the mirror M3 can be input.

As the mirror M3 is arranged in a position optically conjugated to theposition of the neighboring mirror M5, deformations of the reflectionsurface of the neighboring mirror M5 caused, for example, because of athermal expansion of the support body 21 of the neighboring mirror M5can be compensated by deformations in the opposite direction of thereflection surface of the third mirror M3, input by the controlmechanism 25. A deformation of the reflection surface of the neighboringmirror M5 may be detected optically, for example. Correspondingdetection methods are known. The result of this detection of deformationcan then be used as an input signal for the control device 25 todetermine control values for the individual actuators 23.

In this manner, thermal drifts, in particular caused by the differentthermal expansion coefficients of the materials of the support body 21,on the one hand, and of the support bodies 22, on the other hand, can becompensated by a deformation of the reflection surface of the thirdmirror M3. A targeted deformation of the reflection surface of the thirdmirror M3 can naturally also be used to correct or compensate furtherimaging errors, for example for Petzval correction.

The reflection surface of the third mirror M3 may be designed as aclosed reflection surface, sections of this closed reflection surface ineach case being mechanically connected to an individual actuator 23. Itis alternatively possible to equip the third mirror M3 with a reflectionsurface made of a plurality of mirror sections which can be movedseparately from one another, for example as a multi-mirror array or afacet mirror. Each of these mirror sections can then be tilted ordisplaced individually by their own actuator 23, so a deformation of thereflection surface of the third mirror M3 formed by the totality of themirror sections is thus brought about. A deformation of the mirrorsurface of a mirror, which has a highly reflective coating is alsopossible by the use of an electronically actieatable piezo-electriclayer, which may, for example, be arranged between the mirror substrateand the highly reflective coating.

It is possible to use as actuators to deform the third mirror M3 or todeform one of the mirror sections of the third mirror M3, actuatorswhich are described, for example, in U.S. Pat. No. 7,443,619. Lorentzactuators, in particular, can be used. The actuating elements of thethird mirror M3 can be activated at a high band width. This makes itpossible to also compensate deformation imaging influences caused byoscillations or vibrations of the neighboring mirror M5 via thedeformable mirror M3. The deformations of the deformable mirror M3 arethen synchronised with the oscillation deformations of the neighboringmirror M5. This can be realised by a corresponding sensory scanning orsampling of the oscillations of the mirror M5 and activation derivedtherefrom of the actuating elements for the deformable mirror M3.

The reflection surfaces of the mirrors M1 to M6 have rotationallysymmetrical aspherical basic shapes, which can be described by knownasphere equations. Alternatively, it is possible to design at leastindividual ones of the mirrors M1 to M6 as freeform surfaces whichcannot be described by a rotationally symmetrical function. Freeformsurfaces of this type for reflection surfaces of mirrors of opticalprojection systems of projection exposure systems for microlithographyare known from US 2007/0058269 A1 and US 2008/0170310 A1.

The support body 21 of the neighboring mirror M5 can be produced by aCVD (chemical vapour deposition) method. Here, silicon carbide from thegas phase is deposited on a forming body made of graphite. The formingbody in this case has a shape corresponding to the desired reflectionsurface. After the separation of the support body 21 from the formingbody, another coating of the support body 21 can be carried out toimprove the processability and the reflectivity of the reflectionsurface of the support body 21.

As an alternative to a configuration made of a material with a modulusof elasticity, which is at least twice as great as that of one of theother mirrors, the neighboring mirror M5 may also be made of Zerodur® orof ULE® (Ultra Low Expansion) glass. A titanium silicate glass may beused here, for example. Deformations of the neighboring mirror M5 andthe effects thereof on the imaging properties of the imaging opticalsystem 7 may be compensated via the deformable third mirror M3.

FIG. 3 schematically shows a further embodiment of a projection exposuresystem 1. Components, which correspond to those which were describedabove with reference to FIGS. 1 and 2, have the same reference numeralsand are not discussed again in detail.

A collector 26 for collecting the usable emission of the light source 2is arranged downstream of the light source 2. Arranged downstream of thecollector 26 is in turn a spectral filter 27, which is operated ingrazing incidence. A field facet mirror 28 is arranged downstream of thespectral filter 27. A pupil facet mirror 29 is arranged downstream ofthe field facet mirror 28. The concept of facet mirrors 28, 29 of thistype as components of the optical illumination system 6 is basicallyknown, for example, from U.S. Pat. No. 7,186,983 B2.

The pupil facet mirror 29 is arranged in the region of an entry pupilplane 30 of an optical projection system 31, which can be used as analternative to the optical projection system 7 in the projectionexposure system 1. The illumination light 3 is directed by the pupilfacet mirror 29 directly to the reflective reticle 10. No furthercomponent influencing or deflecting the illumination light 3, forexample a mirror with a grazing incidence is present between the pupilfacet mirror 29 and the reticle 10.

The optical projection system 31 is only described below where itqualitatively differs from the optical projection system 7 according toFIGS. 1 and 2.

In the optical projection system 31, the first pupil plane 16 after theobject plane 5 lies between the second mirror M2 and the third mirrorM3. At this point, an aperture diaphragm, for example, may be arrangedto limit the illumination light beam bundle.

The pupil facet mirror 29 and the second mirror M2 of the opticalprojection system 31 are arranged on a connecting axis 32. Thisconnecting axis is defined as the axis passing through the geometriccenter point of the mirror most closely adjacent to the object plane 5and perpendicular to the object plane 5. In the embodiment according toFIG. 3, the mirror M2 is the mirror which is most closely adjacent tothe object plane 5. The second mirror M2 is therefore the mirror, whichis most closely adjacent to the object field 4 along the connecting axis32, of the optical projection system 31. The second mirror M2 isarranged along the connecting axis 32 at a spacing A from the objectplane 5, which is greater than a spacing B of the entry pupil plane 30from the object plane 5. The spacing A is 704 mm. The spacing B is 472mm. The pupil facet mirror 29 and the second mirror M2 of the opticalprojection system 31 are arranged back to back. Therefore, the opticalprojection system 31 provides construction space for accommodating thepupil facet mirror 29 on the connecting axis 32. The pupil facet mirror29 can thus be arranged in such a way that the illumination light 3 fromthe pupil facet mirror 29 is reflected directly to the reflectingreticle 10.

The connecting axis 32 is also perpendicular to the image plane 9. Theconnecting axis 32 also runs through the geometric center point of themirror M5, which is most closely adjacent to the image field 8. Anintersection point C of the connecting axis 32 with the entry pupilplane 30 lies closer to the object plane 5 than a first intersectionpoint D in the beam path of the illumination and imaging light 3 of amain beam 33 of a central object field point with the connecting axis32. Because of the reflecting action of the reticle 10, the entry pupilplane, despite the fact that it is arranged in the beam path upstream ofthe object plane 5, lies between the object plane 5 and the image plane9. Because of the fact that the spacing of the intersection point C fromthe object plane 5 is smaller than the spacing of the intersection pointD from the object plane 5, the possibility is produced of moving thepupil facet mirror 29 into the construction space of the opticalprojection system 31, without an illumination beam path of theillumination light 3 being obstructed by components of the opticalprojection system 31 and without an imaging beam path of theillumination light 3 being obstructed by the pupil facet mirror 29.

In contrast to the optical projection system 7, in the opticalprojection system 31, the spacing of the mirror M3 from the object plane5 is less than the spacing of the mirror M1 from the object plane 5.

The optical projection system 31 has an image-side numerical aperture NAof 0.4. The object field 4, in the optical projection system 31, has anextent of 2 mm in the y-direction and 26 mm in the x-direction. Thereduced imaging scale of the optical projection system 31 is 4×.

The optical data of the optical projection system 31 are reproducedbelow with the aid of two tables in the Code V®-format.

The first table in the “radius” column in each case shows the radius ofcurvature of the mirrors M1 to M6. The third column (thickness)describes the spacing, proceeding from the object plane 5, in each casefrom the following surface in the z-direction.

The second table describes the precise surface form of the reflectionsurfaces of the mirrors M1 to M6, the constants K and A to G beinginserted in the following equation for the arrow height z:

${z(h)}=={{{\frac{{ch}^{2}}{1 + {{SQRT}\left\{ {1 - {\left( {1 + K} \right)c^{2}h^{2}}} \right\}}}++}{Ah}^{4}} + {Bh}^{6} + {Ch}^{8} + {Dh}^{10} + {Eh}^{12} + {Fh}^{14} + {Gh}^{16}}$

h is the spacing here from an optical axis of the optical projectionsystem 31. Thus h²=x²=y² applies. For c, the reciprocal value of“radius” is used.

Surface Radius Thickness Operating mode Object Infinite 1008.515 planeM1 −589.188 −304.940 REFL M2 −241.133 226.892 REFL M3 −1530.294 −188.411REFL M4 557.639 1651.258 REFL M5 1500.000 −509.557 REFL Stop Infinite−745.289 M6 1483.965 1284.846 REFL Image plane Infinite 0.000 Surface KA B C M1 −1.907467E−01 −4.201365E−14  −1.850017E−17 −2.806339E−22 M2−5.642091E−01 1.123646E−08 −1.729255E−13  4.634573E−18 M3 −1.457717E−026.326755E−09  1.214295E−13  7.108126E−18 M4  3.218346E−03 3.917441E−09 1.354421E−13 −2.254336E−17 M5  1.035722E+00 4.337345E−10  9.699608E−16 5.753846E−21 M6  1.041374E−01 −7.896075E−13  −1.157231E−19−3.023015E−25 Surface D E F G M1 4.451266E−27 −5.566664E−32 3.449801E−37−8.987817E−43 M2 2.211189E−21 −1.041819E−24 1.928886E−28 −1.341001E−32M3 −2.395752E−21   8.896309E−31 2.012774E−28 −3.680072E−32 M42.671995E−21  −l.455349E−25 3.081018E−32  2.302996E−34 M5 −2.106085E−25  1.011811E−29 −2.375920E−34   2.279074E−39 M6 1.895127E−30 −6.992363E−361.347813E−41 −1.055593E−47

An overall length of the optical projection system 31, in other wordsthe spacing between the object plane 5 and the image plane 9, in theoptical projection system 31 is 2423 mm. The free working spacing d_(w)of the mirror M5 from the image plane 9 is 30 mm in the opticalprojection system 31. The support body 21 has a maximum thickness of 26mm, so that a free working spacing of 4 mm remains between a rear of themirror 5 remote from the reflection surface of the mirror M5 and theimage plane 9. A maximum diameter of the reflection surface used of themirror M5 in the optical projection system 31 is 300 mm. A ratio betweenthis maximum diameter and the thickness of the support body 21 of themirror M5 is therefore 300/26=11.5.

To produce a microstructured or nanostructured component, in particulara semiconductor component for microelectronics, in other words, forexample, a microchip, the procedure is as follows: firstly, the reticle10 and the wafer 11 are provided. Then, a structure present on thereticle 10 is projected onto a light-sensitive layer of the wafer 11with the aid of the projection exposure system 1. By developing thelight-sensitive layer, a microstructure or nanostructure is thenproduced on the wafer 11.

Corresponding designs of the optical projection system 7, like thataccording to FIG. 2, may also be used in applications other thanprojection exposure, for example as a micro-scope lens system. In thiscase, the object field 4 and the image field 8 exchange their roles. Themirror M5, in other words, the neighboring mirror, in the case ofapplication of the optical projection system 7 as a microscope lenssystem, is then most closely adjacent to the object field 8.

1.-3. (canceled)
 4. An imaging optical system having an object plane andan image plane, the imaging optical system comprising: a plurality ofmirrors configured to image an object field in the object plane into animage field in the image plane, wherein: the plurality of mirrorscomprises a first mirror which, of the plurality of mirrors, is mostclosely adjacent to the object field or the image field; the firstmirror comprises a support body comprising a first material; theplurality of mirrors comprises a second mirror; the second mirrorcomprises a support body comprising a second material; a modulus ofelasticity of the first material is at least twice as great as a modulusof elasticity of the second material; and the imaging optical system isa microlithographic imaging optical system.
 5. The imaging opticalsystem of claim 4, wherein the first material comprises a materialhaving a modulus of elasticity of at least 150 GPa.
 6. The imagingoptical system of claim 4, wherein the first material comprises siliconcarbide.
 7. The imaging optical system of claim 4, comprising adeformable mirror spaced apart from the first mirror.
 8. The imagingoptical system of claim 7, wherein the deformable mirror is arranged ina plane optically conjugated to the arrangement plane of the firstmirror in the imaging optical system.
 9. The imaging optical system ofclaim 4, wherein the second mirror is a deformable mirror.
 10. Theimaging optical system of claim 4, wherein, for at least one of theplurality of mirrors other than the first mirror, the mirror comprises asupport body comprises a material having a thermal expansion coefficientof at most 1×10⁻⁷ m/m/K. 11.-21. (canceled)
 22. The imaging opticalsystem of claim 4, wherein the imaging optical system comprisesprecisely six mirrors.
 23. The imaging optical system of claim 4,wherein a reflection surface of one of the plurality of mirrors is arotationally symmetrical asphere.
 24. The imaging optical system ofclaim 4, wherein a reflection surface of one of the plurality of mirrorsis a freeform surface which cannot be described by a rotationallysymmetrical function.
 25. The imaging optical system of claim 4, whereinat least one of the plurality of mirrors has a through-opening throughwhich the beam path passes.
 26. The imaging optical system of claim 4,wherein the support body of the first mirror is thinner than the supportbodies of the other mirrors
 27. The imaging optical system of claim 4,comprising a plurality of deformable mirrors.
 28. A projection exposuresystem, comprising: an imaging optical system according to claim 4; andan optical illumination system configured so that, during use of theprojection exposure system, the optical illumination system guidesillumination light to the object field of the imaging optical system,wherein the projection exposure system is a microlithography projectionexposure system.
 29. The projection exposure system of claim 28, whereinthe optical illumination system comprises a pupil facet mirror arrangedin the entry pupil plane of the imaging optical system.
 30. Theprojection exposure system of claim 28, wherein the imaging opticalsystem comprises precisely six mirrors.
 31. The projection exposuresystem of claim 28, wherein a reflection surface of one of the pluralityof mirrors is a rotationally symmetrical asphere.
 32. The projectionexposure system of claim 28, wherein a reflection surface of one of theplurality of mirrors is a freeform surface which cannot be described bya rotationally symmetrical function.
 33. The projection exposure systemof claim 28, wherein at least one of the plurality of mirrors has athrough-opening through which the beam path passes.
 34. A method,comprising: providing a microlithography projection exposure system,comprising: an imaging optical system according to claim 4; and anoptical illumination system configured so that, during use of theprojection exposure system, the optical illumination system guidesillumination light to the object field of the imaging optical system;using the microlithography projection exposure system to project astructure on a reticle onto a light-sensitive layer of the wafer; andproducing a microstructure on the wafer.
 35. A microscope lens system,comprising an imaging optical system according to claim 4.